The following acronyms are used in this application.
292M—a STMPE standard
BPSK—binary phase shift keying
CDR—clock and data recovery
DPSK—differential phase shift keying
DRO—dielectric resonating oscillator
FSK—frequency shift keying
GPS—global positioning system
HDSDI—high definition serial interface
HDTV—high definition television
MPEG—Motion Picture Experts Group
OFDM—orthogonal frequency division multiplexing
OQPSK—offset quadrature phase shift keying
QPSK—quadrature phase shift keying
SMTPE—Society of Motion Picture and Television Engineers
Wireless cameras have been used for live broadcast of television to provide coverage of events in remote or urban locations. Typically the camera transmits compressed data to a nearby vehicle which then re-transmits the data through a satellite link.
Current technology allows for capture and digitization of video conforming to the high-definition television (HDTV) standard. The video data is compressed using an encoding method such as MPEG 2, which greatly reduces the necessary bandwidth of the wireless link. Methods such as OFDM can be used to overcome multipath, and the modulated waveform can then be used to transmit the data in an unlicensed band such as the 2.4 or 5.8 Ghz ISM band.
It is possible to mount two or more HDTV cameras side by side to obtain multi-view video. If the video data is reproduced live at a remote location, this can give the viewer the sensation that he is present at the live location. For example, if two cameras are placed next to each other, the resulting HDTV stream can be used to reproduce three-dimensional (3-D) television. In order for the 3-D effect to be experienced by the viewer, the timing relationship between the two video streams must be preserved.
Current wireless systems for digital television compress the video signal using MPEG 2 or similar compression methods. With multi-view video, this compression results in the loss of the interrelationship and synchronization between the individual channels. In order to preserve the timing relationship between the multiple video streams, and to allow for other processing, which sometimes cannot be done at the same location as the camera, it is necessary to transmit uncompressed HDTV video data from one or multiple cameras. The uncompressed data rate for digital HDTV is typically 1.485 Gbps, in accordance with the SMPTE 292M standard. For the transmission of multi-view HDTV, multiple 1.485 Gbps data streams would be required. For 3-D HDTV broadcasting, it would be necessary to transmit two, 1.485 Gpbs data streams with an aggregate throughput of nearly 3 Gbps.
Typically, such high throughputs can only be handled using coax or fiber optic cable. However, these cables encumber the camera operator who must be able to move continuously, and require significant advance preparation. In some venues such as field events or in crowded environments it is not feasible to use a camera tethered with a cable. A wireless system is needed to transmit the digital video from the camera location to a second relay station which would be at least 100 yards away which would then send the data via optical fiber or satellite link. Conventional wireless links in the 2.4 Ghz and 5.3 Ghz unlicensed bands cannot support such high data rates. Microwave systems above 50 GHz which can support such throughput require rigid platforms, precise pointing, and are not well suited to a man-mounted, portable system.
Development of a wireless video camera capable of transmission of uncompressed high definition digitized video represents a great improvement in the field of video engineering and satisfies a long felt need of video engineers, producers and directors.